During flight, the control of aerodynamic vehicles, such as aircraft, is principally accomplished via a variety of flight control effectors. These flight control effectors include aerodynamic controls such as the rudder, elevators, ailerons, speed brakes, engine thrust variations, nozzle vectoring and the like. By altering the various flight control effectors, the system state vector that defines the current state of the aerodynamic vehicle can be changed. In this regard, the system state vector of an aerodynamic vehicle in flight typically defines a plurality of current vehicle states such as the angle of attack, the angle of side slip, the air speed, the vehicle attitude and the like.
Historically, the flight control effectors were directly linked to various input devices operated by the pilot. For example, flight control effectors have been linked via cabling to the throttle levers and the control column or stick. More recently, the flight control effectors have been driven by a flight control computer which, in turn, receives inputs from the various input devices operated by the pilot. By appropriately adjusting the input devices, a pilot may therefore controllably alter the time rate of change of the current system state vector of the aerodynamic vehicle.
Unfortunately, flight control effectors may occasionally fail, thereby adversely affecting the ability of conventional control systems to maintain the dynamic stability and performance of the aerodynamic vehicle. In order to accommodate failures of one or more of the flight control effectors, control effectors failure detection and flight control reconfiguration systems have been developed. These systems typically remove the flight control effectors that have been identified as inoperable from the control system. These systems are therefore designed to detect the failure of one or more flight control effectors and to alter the control logic associated with one or more of the flight control effectors that remain operable in an attempt to produce the desired change in the time rate of change of the current system state vector of an aerodynamic vehicle requested by the pilot. These failure detection and flight control reconfiguration systems are highly complex. As such, the proper operation of these systems is difficult to verify. Moreover, these systems introduce a risk that a flight control effector that is actually functioning properly may be falsely identified as having failed and thereafter removed from the control system, thereby potentially and unnecessarily rendering the control system less effective.
Additionally, the control effectors of an aerodynamic vehicle generally have some limitations on their performance. In this regard, the rate of change accommodated by most control effectors is generally limited to a range bounded by upper and lower limits. By way of example, for aircraft, such as direct lift aircraft, that permit nozzle vectoring, the actual position which the nozzles may assume is typically limited to within upper and lower limits. Unfortunately, conventional control systems do not accommodate limitations in the range of settings and rate of change of the control effectors. As such, conventional control systems may attempt to alter a control effector in a manner that exceeds its limitations. Since the control effector will be unable to make the desired change, the control system may correspondingly fail to produce the desired change in the time rate of change of the system state vector of the aircraft.
In addition to the aerodynamic surfaces commonly utilized to control the flight of an aerodynamic vehicle, aircraft has been developed that can provide additional control by means of thrust variations and/or thrust or nozzle vectoring. For example, some multi-engine aircraft permit the plurality of engines to be driven differently so as to generate different levels of thrust which, in turn, can serve to assist in the controlled flight of the aircraft. As another example, vectoring nozzles that may be commanded to assume any of a range of positions and bi-directional nozzles that direct the exhaust in one of two directions have been developed. By controllably directing at least a portion of the engine exhaust in different directions, vectoring nozzles, which shall hereafter also generally include bi-directional nozzles, can also assist in the controlled flight of the aircraft.
While various control systems have been developed to control the flight control effectors during flight, these control systems generally do not integrate the control provided by aerodynamic surfaces during flight with the control needed in instances in which the aircraft has no, or a negligible, velocity such that the aerodynamic control surfaces, such as the rudder, elevators, ailerons or the like, do not significantly contribute, if at all, to the lift and attitude control of the aircraft. In this regard, direct lift aircraft have been and are being developed. Direct lift aircraft have control effectors, such as vectoring nozzles or bi-directional nozzles, that can direct the engine exhaust in different directions to provide lift and attitude control of the aircraft. By appropriately positioning the nozzles, a direct lift aircraft can takeoff and land in a substantially vertical manner. As such, during takeoff and landing, the aerodynamic control surfaces do not significantly contribute to the lift and the attitude control of the direct lift aircraft. Instead, the lift and attitude control are principally provided and controlled by any thrust variations provided by the engines and the vectoring of the associated nozzles.
In order to control the lift and attitude of an aircraft during a vertical takeoff or landing, control systems have been developed to control the engines and the associated nozzles. For example, one control system employs an optimization algorithm, termed an L1 optimization algorithm. While generally effective, this optimization algorithm suffers from several deficiencies. In this regard, the optimization algorithm is computationally complex, thereby requiring substantial computing resources and being difficult and costly to expand or scale to accommodate more sophisticated control schemes, such as the control scheme necessary to control vectoring nozzles as opposed to simpler bi-directional nozzles. The computational complexity of the optimization algorithm may also cause the solution to be approximated in instances in which the optimization algorithm cannot arrive at an exact solution within the time frame required to maintain stability of the aircraft. In addition, the optimization algorithm may not converge in all situations. In instances in which the optimization algorithm may not converge, the prior solution, i.e., the solution from a prior iteration of the optimization algorithm, would continue to be utilized, thereby resulting in a sub-optimal solution.
As such, it would be desirable to provide an improved control system that effectively integrates the various control effectors including the aerodynamic surfaces and the thrust variations and nozzle vectoring so as comprehensively control the aerodynamic vehicle during different stages of flight, including for example, the vertical takeoff and landing of a direct lift aircraft during which thrust variations and nozzle vectoring dominate the control scheme as well as in flight during which the aerodynamic surfaces provide a greater measure of control. In addition, it would be desirable to develop a method of controlling the control effectors of an aerodynamic vehicle, such as a direct lift aircraft, which provides increased flexibility with respect to the removal or inclusion of a flight control effector that may have failed. In addition, it would be advantageous to provide a method for controlling the control effectors of an aerodynamic vehicle, including a direct lift aircraft, in a manner that recognizes and accommodates limitations in the settings and rate of change of at least some of the control effectors.